WO1995024318A1

WO1995024318A1 - Dispersion of microcapsules

Info

Publication number: WO1995024318A1
Application number: PCT/EP1995/000613
Authority: WO
Inventors: Bodo Hilterhaus; Günter GABEL
Original assignee: Stora Feldmühle Ag
Priority date: 1994-03-09
Filing date: 1995-02-21
Publication date: 1995-09-14
Also published as: ES2127512T3; CZ285796B6; EP0749371B1; CZ258296A3; EP0749371A1; DE4407813C1; DE59504421D1

Abstract

The microcapsules of a dispersion for producing pressure-sensitive printing papers contain as solvent 10 to 30 % by weight of a liquid paraffin oil at room temperature, 25 to 60 % by weight of a liquid vegetable oil at room temperature or 15 to 60 % by weight of a mixture of 5 to 30 % by weight of a liquid paraffin oil at room temperature and 10 to 55 % by weight of a liquid vegetable oil at room temperature, the balance consisting of a solid or semi-solid vegetable oil at room temperature. The solvent contained in the core of the capsules is liquid at room temperature and the capsule wall is made of polycarbamide.

Description

Microcapsule dispersion

The present invention relates to a microcapsule dispersion for producing pressure-sensitive recording papers, in which the core solvent contained in the microcapsules is a dye precursor or a

Contains dye precursor mixture and a vegetable oil that is solid or semi-solid at room temperature.

Microcapsule dispersions of the type mentioned at the outset and their use have been known for a long time. Essentially two different types of capsule wall-forming materials are used, namely water-soluble capsule wall-forming materials, such as. B. pig skin gelatin, gum arabic and water-insoluble, such as. B. polyisocyanate as one of the components used for the production of polyurea capsules. The microcapsule dispersions are also spacers, for. B. starch granules or cellulose fibers and a suitable binder for fixing the microcapsules on the paper surface. A large number of proposals are known from the known prior art which relate to suitable solvents or oils and their mixtures for taking up the color precursor compounds. For the sake of simplicity, this microcapsule component is referred to below as the core solvent.

From DE-A-22 51 350 diphenylalkanes, alkyl-substituted diphenylalkanes, diphenylalkenes and / or alkyl-substituted diphenylalkenes are known as liquid core solvents for dye precursors. For dilution, 3 parts of diluent, u. a. Paraffin oil, castor oil, claw oil, olive oil, soybean oil, cottonseed oil, coconut oil or rapeseed oil or organic solvents such as aromatic gasoline or alkylbenzene can be used. The addition of these diluents is intended to change the physical properties, such as the viscosity and the vapor pressure, with the aim of better manageability or for process reasons.

DE-A-26 40 197 relates to a preparation for dissolving dye formers for pressure-sensitive copying systems in which the color acceptors consist of acidic resins. According to that invention, a mixture of partially hydrogenated terphenyl and alkylbenzene components which is liquid at room temperature is used, optionally with up to about 3 parts of diluent for each part of solvent can be moved. Liquid mineral oils or vegetable oils, but also coconut oil solid at room temperature, are mentioned as diluents.

In recent developments, vegetable, animal and physiologically harmless mineral oils have been increasingly used.

EP-A-0 262 569 provides as the core solvent a composition which consists of at least 80% by weight of vegetable, animal or paraffin oil, a dye precursor based on a triphenylmethane leuco dye being used and the wall material of the microcapsules being water-soluble or prior to microcapsule formation is water dispersible.

EP-A-0 520 639 also provides a core solvent which contains a vegetable oil for a microcapsule to be used for the production of pressure-sensitive recording paper. As a further constituent, an ester component of a non-aromatic monocarboxylic acid with a saturated or unsaturated straight or branched hydrocarbon chain with at least 3 carbon atoms in the chain is also provided in this composition.

In contrast, EP-A-0 573 210 proposes a core solvent which does not contain the aforementioned ester component, the as Vegetable oil provided for the core solvent has a softening range of approximately 20 to 25 degrees and consists at least for the most part of a vegetable oil that is solid or semi-solid in this temperature range. However, this proposal is not free from disadvantages.

It has been shown that polyisocyanate, as a component to be used for the production of polyurea capsules, is soluble or at least excellently dispersible in vegetable oils which are solid or semi-solid at room temperature, and is therefore at the same time suitable for the organic solvents previously required to dissolve this component, such as. B. isopropylnaphthalene, can be dispensed with. However, studies carried out by the inventors of the present application have shown that solid or semi-solid core solvent mixtures in a temperature range close to room temperature can lead to production disturbances in the production of capsules from polyurea. These disadvantages do not occur in the production of microcapsules on a laboratory scale using stirrer vessels, but they are immediately noticeable when a dispersion unit consisting essentially of a dispersing head, cooling device and pipelines connecting these elements is used in continuous or discontinuous production operation, in which the Formed core solvent droplets through pipes from the dispersing head to the cooling device be directed. On the parts of the cooling device which are acted upon by cooling water, solidification and, as a result, deposits of oil mixtures which have a relatively high softening range can occur. The maintenance of a perfect microcapsule dispersion is permanently impaired.

Based on the disadvantages identified, the object of the invention is to provide a

To provide microcapsule dispersion which, because of the core solvent components used, enables problem-free capsule production. At the same time, only oils of vegetal origin should be used predominantly. Another task is to provide a microcapsule with high tightness, for which purpose polyurea is to be used as the capsule wall material which has proven itself in this regard.

To achieve the object, the invention therefore provides a microcapsule dispersion which can be used for the production of pressure-sensitive recording papers and in which the core solvent contained in the microcapsules is a dye precursor or a

Contains dye precursor mixture and a vegetable oil which is solid or semi-solid at room temperature, characterized in that

- 10 to 30% by weight of the core solvent from a paraffin oil which is liquid at room temperature or> 25 up to 60% by weight from a vegetable oil liquid at room temperature or

15 to 60% by weight from a mixture of 5 to 30% by weight of a paraffin oil which is liquid at room temperature and 10 to 55% by weight of a vegetable oil which is liquid at room temperature,

- rest: a vegetable oil which is solid or semi-solid at room temperature;

- The core solvent is liquid at room temperature and

- The capsule wall material consists of polyurea.

The term "room temperature" used in the description and in the claims means that the core solvent is liquid above 20 ° C. The term "liquid" means: flowable.

Among the paraffin oil specified in the description and claims of the present application are naphthenic or paraffin-based mineral oil products, e.g. B. white oil and spindle oil to understand. Chlorine paraffin, which has already been proposed several times as the core solvent, is not encompassed by the present invention.

In order to establish a liquid state in the core solvent, smaller quantities of paraffin oil are sufficient than of liquid vegetable oil. If liquid paraffin oil is used as the sole additive to a core solvent, which consists of solid or semi-solid vegetable oil Amounts of at least 10% by weight are required, preferably not more than 20% by weight. When using liquid vegetable oils, the minimum amount added is more than 25% by weight and can be up to 60% by weight. Mixtures of liquid paraffin oil with liquid vegetable oil on the one hand and solid or semi-solid vegetable oil on the other hand are also possible; an amount of paraffin oil below 10% by weight can also be used here, but then higher amounts of liquid vegetable oil than this sole use of liquid paraffin oil would have to be added.

According to a preferred embodiment of the invention, the core solvent consists of 80 to 90% by weight of a vegetable oil which is solid or semi-solid at room temperature, the rest: a paraffin oil which is liquid at room temperature. A preferred core solvent mixture consisting of only vegetable oils consists of 60 to 70% by weight of a vegetable oil that is solid or semi-solid at room temperature, while the rest consists of a vegetable oil that is liquid at room temperature. According to the invention, coconut oil, palm oil and palm kernel oil or mixtures of these oils are preferred as solid or semi-solid vegetable oils. Rapeseed oil, sunflower oil, cottonseed oil, olive oil, corn oil, safflower oil or a mixture of these oils are preferred as vegetable oils which are liquid at room temperature. Furthermore, a color precursor mixture is preferred which contains 2-phenyl-4- (4-diethylaminophenyl) -4- (4-methoxyphenyl) -6-methyl-7-dimethylamino-4H-benz.3.1-oxazine as color former. Such a color former mixture has good solubility in the core solvent mixtures provided according to the invention, while on the other hand a high efficiency of the microcapsule dispersion according to the invention is also ensured.

According to the invention it is further provided that the core solvent contained in the microcapsules does not solidify at temperatures of more than 18 ° C.

Spacers, binders and coating aids can be added to the microcapsule dispersion. These measures, like the application of the microcapsule dispersion to a suitable coating base paper and the application method used, are not an object of the present invention.

The following examples illustrate the invention:

Examples 1 and 2:

Preparation of a microcapsule dispersion: In a mixture of 90 parts by weight of coconut oil (Cocopur from Rau) and 10 parts by weight of paraffin oil (white oil P 1020 from Parafluid) is a dye precursor mixture consisting of 60 parts by weight. Share 2-phenyl-4- (4-diethylaminophenyl) -4- (4-methoxyphenyl) -6-methyl-7-dimethylamino-4H-benz .3.1-oxazine (baymicron SN 2601 from BAYER, see also claim 7 of the EP A-0 573 210), 20 parts by weight of a fluorine-based dye precursor and 20 parts by weight of CVL so that a

Dye concentration of 6% is present in the core solvent.

71 g of diisocyanate are added to 447 g of the color image mixture produced, and 992 g of a 1% strength polyvinyl alcohol solution (as an emulsifying aid) in demineralized water are subsequently added. The mixture produced is transferred to the storage vessel of a pilot encapsulation plant. The dispersion head of the dispersion unit, which is connected to a cooling device by a pipeline, is then filled and the dispersion is initiated. After the water-cooled cooling device has been passed through, part of the liquid leaves the dispersing unit via a throttle disc and is guided to a separate stirring vessel, while another part of the liquid is fed again to the dispersing head in the circuit. A 5.4% solution of diethylenetriamine (DET) in demineralized water and, if necessary, defoamer are added to the separate stirred vessel. The temperature set in the separate mixing vessel is 25 ° C. Capsules with an average size of 5.1 μm are formed. 8.6% of the capsules were> 10 μm in size. Using the same

Dye precursor mixture, as stated above, but with an oil mixture in which the white oil content was 20 parts by weight, a microcapsule dispersion was produced under the same process conditions, giving an average grain size of 5.9 μm and 15.8% of the microcapsules were> 10 μm.

After the end of the experiment, settling of the core solvent mixtures on the cooling device was not observed in either of the two cases.

15% by weight of cellulose fibers were added to the microcapsule dispersion as spacers and 17% by weight, calculated as parts by dry weight, based on the total solids content of the microcapsule coating color, of an oxidized starch solution as a binder. The prepared microcapsule coating color was then spread onto a conventional coating base paper using a wire doctor coating device with an application weight of 5.5 g / m ² and dried. The CB sheet produced was labeled in contact with a conventional CF sheet. The result was a legible copy with improved light stability. Further investigations showed an improved tightness and high light stability of the capsule. Examples 3 to 4 and Comparative Example:

The following examples serve to demonstrate that the core solvent mixtures according to the invention are comparable in terms of the stability of the capsule or the intensity of the typeface in terms of the capsule tightness and in terms of aging resistance to the pressure-sensitive recording papers known from the prior art - EP-A-0 573 210 .

The dye precursor mixture described for Examples 1 and 2 was used and a dye concentration of 6% was set in the core solvents given below. The microcapsules were produced as indicated for Examples 1 and 2, and the microcapsules produced were used to produce CFB sheets on a wood-free, mass-coated coating base paper of 42 g / m ² , which already had a CF layer on one side was provided, in which the color acceptors consisted of acidic clays, applied to the side opposite the CF layer while setting a coat weight of 6 g / m ² . In addition to the microcapsules, the coating color also contained ground cellulose as a spacer and butadiene styrene latex as a binder. The microcapsule dispersion was applied using a doctor blade. Composition of the core solvents:

Comparative example:

100% coconut oil according to EP-A-0 573 210

Coconut oil type as in Example 1

Example 3:

90% coconut oil as in comparative example

10% white oil as in example 1

Example 4:

80% coconut oil as in comparative example

20% white oil as in example 1

Role test:

This test is used to check capsule stability when exposed to different pressures.

The Dürner test pressure device was used. Sample strips of 24 x 4.5 cm of the CFB sheets produced were combined with sample strips from a further CF sheet so that the CB side is adjacent to the CF side. The test specimens were subjected to 3 defined pressures between an aluminum roller and a blanket holder. The drop in brightness of the CF sheet was measured. The test results obtained are shown in the table below: Test result: role test

Print Comparative Example 3 Example 4

20 kp 3 3 4

50 kp 8 7 9

70 kp 12 13 12

Higher numerical values correspond to a stronger discoloration. In the present case, the values determined for the same pressure load (20, 50 or 70 kp) are so close together that a differentiation is not possible.

Stack test:

This test serves to check the capsule tightness.

DIN A5 samples of the CFB sheets according to comparative example and examples 3 and 4 are placed over a standard CF sheet and loaded with 500 g, based on the area indicated. The aging took place for 6 days at 70 ° C. and in an atmosphere set to 75% relative humidity. The discoloration on the CF layer of the CF sheet caused by color former migration from damaged or defective microcapsules from sheet to sheet is assessed. According to the visual assessment of the CF sheet, no differences can be determined between the samples.

Aging:

CFB sheets according to comparative example and examples 3 and 4 are stored for 12 days at 70 ° C. and 75% relative atmospheric humidity in the dark. The aged samples are combined with a standard CF sheet and labeled. The image intensity is then determined in comparison to an unaged sample. The result is shown in the table below.

Aging

Comparative Example 3 Example 4

96% 97% 95%

As the table shows, the values are so close together that a differentiation is not possible.

Annotation:

The child aging described under 3 of the present test report essentially corresponds to the "accelerated aging" given on page 7, lines 15 ff. Of EP-A-0 573 210, with the difference that according to EP-A -0 573 210 the CF discoloration of the CFB sheet and not the loss of writing power is assessed.

Copy aging:

The copies of the CFB sheets according to Comparative Example and Examples 3 and 4 on a CF sheet were exposed to a daylight lamp for 6 days and the decrease in intensity, based on the starting intensity, was determined. No differences between the capsules can be determined here either.

Comparative Example 3 Example 4

75% 75% 76%

It was thus demonstrated that the use of the core solvent mixture according to the invention has no adverse effect on the writing performance and the aging resistance compared to the pressure-sensitive carbonless papers known from EP-A-0 573 210.

Claims

claims

Microcapsule dispersion for the production of pressure-sensitive recording papers, in which the core solvent contained in the microcapsules contains a dye precursor or a dye precursor mixture and a vegetable oil which is solid or semi-solid at room temperature, characterized in that

- 10 to 30% by weight of the core solvent from a paraffin oil which is liquid at room temperature or> 25 to 60% by weight of a vegetable oil which is liquid at room temperature or

- rest: a vegetable oil which is solid or semi-solid at room temperature;

- The core solvent is liquid at room temperature and

- The capsule wall material consists of polyurea.

2. Microcapsule dispersion according to Claim 1, characterized in that the core solvent consists of 80 to 90% by weight of a vegetable oil which is solid or semi-solid at room temperature, the rest: paraffin oil which is liquid at room temperature.

3. Microcapsule dispersion according to Claim 1, characterized in that the core solvent consists of 60 to 70% by weight of a vegetable oil which is solid or semi-solid at room temperature, the rest: a vegetable oil which is liquid at room temperature.

4. Microcapsule dispersion according to one of claims 1 to 3, characterized in that the core solvent contains coconut oil, palm oil and palm kernel oil or a mixture of these oils as a solid or semi-solid vegetable oil at room temperature.

5. Microcapsule dispersion according to one of claims 1 to 4, characterized in that the core solvent contains rapeseed oil, sunflower oil, cottonseed oil, olive oil, corn oil, safflower oil or a mixture of these oils as a vegetable oil which is liquid at room temperature.

6. Microcapsule dispersion according to one of claims 1 to 5, characterized in that a 2-phenyl-4- (4-diethylaminophenyl) -4- (4-methoxyphenyl) -6-methyl-7-dimethylamino-4H-benz in the core solvent. 3.1-oxazine as Color precursor mixture is included.

7. Microcapsule dispersion according to one of claims 1 to 6, characterized in that the core solvent contained in the microcapsules does not solidify at temperatures of more than 18 ° C.